The surge of leakage, or photo current, that occurs in an integrated circuit during exposure to a high level burst of ionizing radiation (often referred to a transient radiation) can cause a reduction in the supply voltage internal to the integrated circuit. In extreme cases, this reduction in supply voltage, commonly referred to as rail span collapse, can cause loss of information stored in latches or memory arrays, or cause malfunction of logic circuits. Low voltage applications are particularly susceptible to rail span collapse because of their smaller theoretical dynamic range. Thus, a much smaller current leakage level will adversely impact a low voltage device than other devices. Generally, it is preferable to stop operation of the circuit rather than corrupt stored information. Further, it is desirable to protect stored information when the circuit is in standby.
Many methods have been developed to reduce data corruption when an integrated circuit is exposed to transient radiation. Most of them involve improved ways to manufacture individual elements (i.e., transistors, etc.) or ways to detect transient dose conditions. However, there is a need for improved ways to limit current especially for low voltage applications.
CMOS circuits generally have low standby current. However, accumulated exposure to ionizing radiation can increase leakage. Also, leakage currents may increase as threshold voltages are lowered to retain performance with reduced power supply voltages. Therefore, there is also a need to reduce standby current in CMOS circuits.